1. Field of the Invention
The present invention relates to an optical measurement apparatus and an optical measurement system that enable reduction of measurement errors due to variation in the distribution of light emitted from an optical fiber, as well as a fiber coupler directed thereto.
2. Description of the Background Art
A technique of measuring optical characteristics of an object to be measured, by means of a spectroscopic optical system, has conventionally been known. More specifically, where the object to be measured is a light emitting body (light source), spectrum, light source color, brightness, illuminance, and quantum efficiency, for example, of the light emitted from the object are measured. Further, where the object to be measured is a non-light-emitting body, reflectance or transmittance, and/or absorbance, for example, is measured, based on the reflected light or transmitted light obtained from irradiation of the object with light. Further, in some cases, from the optical characteristics thus measured, a physical amount such as the film thickness of the object to be measured is calculated.
Methods of reducing measurement errors in such spectroscopic measurement have been proposed. For example, Japanese Patent Laying-Open No. 01-124723 discloses a configuration that enables reduction of measurement errors due to wavelength-dependent polarization characteristics.
In contrast to the use of spectroscopic measurement as described above, a configuration in which an integrating sphere is used as a light source apparatus to homogenize or mix the light from a light source has been known (for example, Japanese Patent Laying-Open Nos. 60-202411, 63-285441, and 07-212537, Japanese National Patent Publication No. 2003-527619, Japanese Patent Laying-Open No. 2005-055571, and U.S. Patent Application Publication US2005/0156103A1).
Spectroscopic measurement could involve, in addition to measurement errors due to polarization characteristics as described above, measurement errors due to variation of the light distribution. Typically, while light to be measured propagates in an optical fiber, variation of the transmittance could cause variation in the distribution of the light emitted from the optical fiber. Such variation of the light distribution results in uneven brightness on a light-receiving surface of a spectroscopic measurement device.
In the case where a plurality of light rays to be measured are propagated through a plurality of optical fibers respectively and measured with a common spectroscopic measurement device, these optical fibers have to be optically coupled to one optical fiber. In such a case, if variation of the light distribution occurs as described above, the amount of optical coupling varies, which results in a problem that the amount of light for example directed to the spectroscopic measurement device also varies.